1. Field of the Invention
The instant invention pertains generally to semi-automated warehousing systems for transferring unitized loads to, from, and within, the system. More particularly, the instant invention relates to significant improvements in the stacker crane and transfer vehicle used to implement the warehousing system.
2. Discussion of Prior Art
One approach to effectively handling the increased demand for warehousing systems for unitized loads borne upon pallets has focused upon completely automated warehousing systems including multiple mobile lifts traveling at high speeds, numerous transfer vehicles operatively associated therewith, and computerized controls, including a central data processor, on-board computers and means for optically scanning lane and tier markers during high-speed travel, for accurately depositing, or removing, a load-carrying pallet from a selected location on a storage rack. Such complex systems, while potentially increasing the through-put capacity of the warehousing system, have posed problems, such as significantly expanded capital costs for system installation related to the close tolerances that must be maintained within the system, inflated maintenance and operational costs and increases in "down-time" attributable to the need to utilize specially trained computer technicians for repair calls.
Also, since the transfer vehicles operatively associated with most mobile lifts can only service as storage position adjacent to the lift, several expensive lifts are required and a considerable amount of warehousing space must be surrendered for aisle space within which the lifts will travel. Some known automated warehousing systems attempt to save aisle space by replacing the transfer vehicles with shuttle tables, telescoping loading forks, or the like, that can service two pallet positions on each side of the aisle. However, such shuttle tables and telescoping loading forks are complex in construction, and expensive to operate and maintain.
The complexity of the control circuitry required for automated warehousing systems may be better appreciated by an inspection of U.S. Pat. No. 3,938,081, granted Feb. 10, 1976, to Robert T. Kirk while the limitations of the shallow rack storage capacity may be better appreciated by a review of U.S. Pat. Nos. 3,866,767 and 3,880,299, granted Feb. 18, 1975 and Apr. 29, 1975, to Howard A. Zollinger and LeRoy Lubbers, and to Howard A. Zollinger, LeRoy Lubbers and William K. Stubbs, respectively.
Another solution to the problem of attaining high-throughput warehousing has been proposed in U.S. Pat. No. 3,800,963, granted Apr. 2, 1974 to Edward T. Holland. Such warehousing system, which may be broadly characterized as a semi-automatic system, relies upon an operator positioned in the cab on a stacker crane to visually observe, and manually control, the operation of a carrier that can be extended laterally away from the crane to deposit or retrieve a pallet from any storage lane and tier. In effect, the reasoning power of the operator replaces the decision-making capability built into the computer network associated with the above-described automated warehousing system.
Although the system disclosed in the Holland patent admits of greatly reduced installation and operational costs, and yet possesses the capacity to service two storage areas that are several pallets in depth from a single aisle, the location of the cab on the stacker crane limits the visibility of the operator. Also, the transfer vehicle is physically joined to the host vehicle as by a control-power cord, or belt. The dual cord poses significant problems since it must be kept taut at all times by a take-up mechanism, lest the cord interfere with the movement of the carrier in the storage rack; the constant winding and unwinding of the cord (especially in refrigerated environments), more often than not, results in breaking of the electrical conductors in the cord requiring replacement thereof at considerable cost and down-time of the system. Also, the cord had to be fabricated as a wide, thin belt to accommodate a plurality of electrical leads for power and other leads for control purposes; the belt had to be encased in an abrasion resistant coating.
To circumvent the problems associated with the control-power cord used in the semi-automated system shown in the Holland patent for energizing the transfer vehicle and furnishing control signals thereto, attempts were made to produce a battery powered transfer vehicle. Such vehicle would retain the mobility to service "deep storage" racks, and yet not be encumbered by an expensive and troublesome dual cord, also known in the trade as an umbilical cord. One such battery powered transfer vehicle is shown in U.S. Pat. No. 3,869,028, granted Mar. 4, 1975 to Yuji Sawada et al. The battery in the transfer vehicle is charged via a power line and an electrified shoe whenever the vehicle returns to its home station. The charging of the battery insures a fully effective source of power; also, insulation within the vehicle retains the heat imparted thereto so that the vehicle can operate for extended periods of time within cold storage warehouses without significant diminuition of the electrical potential of the battery.
However, Sawada et al relies upon an electrolytic battery that required an air intake pipe and a hydrogen gas exhaust pipe to release the excess gas produced by the recharging operation to the exterior of the warehouse, lest a spark ignite the hydrogen gas. If the hydrogen gas is not purged, the build-up may have a harmful impact on the performance of the battery.